Auditory pattern perception by human and nonhuman primates is mediated by neurons in superior temporal cortex that alter their electrophysiological behavior in response to acoustic signals (Walzl & Woolsey 1943; Katuski et al. 1962; Celesia 1976; Heffner & Heffner 1986; Tramo et al. 1990; Liegeois-Chauvel et al. 1994; Peretz et al. 1995; Colombo et al. 1996). The proposed research investigates how the distinctive spectrotemporal patterns of different vocal communication signals are encoded in the discharge patterns of auditory cortical neurons. Specifically, the timing and magnitude of neuronal excitation and inhibition will be analyzed in alert Macaca mulatta with respect to the acoustical features and behavioral contexts of species-specific vocalizations. the experimental design takes advantage of 1) homologies between humans and macaques in certain aspects of auditory cortex anatomy and function; 2) the rich vocal repertoire of rhesus monkeys; 3) previous and concurrent characterizations of natural communication behavior and perceptual functions in macaques by the Co-Principal Investigators; 4) the high probability, magnitude, and temporal complexity of neuronal responses to natural sounds in the absence of general anesthesia; and 5) insights gained during our initial experimental observations (Tramo et al. 1996).